Screw Compressor

ABSTRACT

A screw compressor is provided which can reduce the pressure loss in a suction flow passage. A casing  12  of the screw compressor includes a bore  21  that accommodates a lobed portion  13 A of a male rotor  11 A and a lobed portion  13 B of a female rotor  11 B therein such that working chambers are formed in lobe grooves of the lobed portions, a suction port  22  located on an outer side in a rotor radial direction, and a suction flow passage  23  that communicates in a rotor axial direction with working chambers that are in a suction stroke. The suction flow passage  23  includes a male rotor side suction flow passage  26 A located on an male rotor  11 A side and besides on a downstream side with respect to a virtual plane C, and a female rotor side suction flow passage  26 B located on an female rotor  11 B side and besides on the downstream side with respect to the virtual plane C. The male rotor side suction flow passage  26 A is formed such that a flow passage wall  27 A on the outer side in the rotor radial direction is located at a position that is the same as that of a wall of the bore  21  as viewed in the rotor axial direction at least within a range of one half of an axial pitch P 1  of the lobed portion  13 A of the male rotor  11 A from a suction side end surface of the lobed portion  13 A in the rotor axial direction.

TECHNICAL FIELD

The present invention relates to a screw compressor including a suction port positioned on the outer side in a rotor radial direction and a suction flow passage that communicates in a rotor axial direction with a working chamber.

BACKGROUND ART

The screw compressor described in Patent Document 1 includes a male rotor having a lobed portion, a female rotor having a lobed portion that engages with the lobed portion of the male rotor, and a casing that accommodates the male rotor and the female rotor therein.

The casing has a bore that accommodates the lobed portion of the male rotor and the lobed portion of the female rotor therein such that working chambers on the male rotor side and working chambers on the female rotor side are formed in lobe grooves of the lobed portions. Further, the casing has a suction port located on the outer side in a rotor radial direction with respect to the lobed portion of the male rotor and the lobed portion of the female rotor, and a suction flow passage formed so as to connect the suction port to the working chambers that are in a suction stroke. The casing further has a discharge port located on the outer side in the rotor radial direction from the lobed portion of the male rotor and the lobed portion of the female rotor, and a discharge flow passage formed so as to connect the discharge port to the working chambers that are in a discharge stroke.

The working chamber is changed in volume while moving from one side to the other side in the rotor axial direction. Consequently, the working chamber sequentially performs a suction stroke for sucking gas from the suction port through the suction flow passage, a compression stroke for compressing the gas, and a discharge stroke for discharging the compressed gas to the discharge port through the discharge flow passage.

The suction flow passage communicates in the rotor axial direction with the working chambers that are in the suction stroke. Further, the suction flow passage includes a male rotor side suction flow passage provided on the male rotor side and besides on the downstream side with respect to a virtual plane that passes a central axis of the male rotor and a central axis of the female rotor (in other words, on the opposite side to the suction port), and a female rotor side suction flow passage provided on the female rotor side and besides on the downstream side with respect to the virtual plane described above.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-2012-041910-A (for example, refer to FIGS. 8 and 9)

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In Patent Document 1, a flow passage wall on the outer side in a rotor radial direction of the male rotor side suction flow passage (except a portion for confining gas to the working chamber) is located on the outer side in the rotor radial direction with respect to the wall of the bore. Therefore, as a component of a flow of the gas flowing from the male rotor side suction flow passage toward the male rotor side working chamber, a component in the rotor radial direction appears, and this makes a cause of increase in pressure loss.

Similarly, a flow passage wall on the outer side, in a rotor radial direction, of the female rotor side suction flow passage (except a portion for confining gas to the working chamber) is located on the outer side in the rotor radial direction with respect to the wall of the bore. Therefore, as a component of a flow of the gas flowing from the female rotor side suction flow passage toward the female rotor side working chamber, a component in the rotor radial direction appears, and this makes a cause of increase in pressure loss.

The present invention has been made in view of such matters as described above, and reducing the pressure loss in a suction flow passage is one of subjects of the present invention.

Means for Solving the Problem

In order to solve the problem described above, the configuration described in the claims is applied. The present invention includes a plurality of means for solving the problem described above, and an example of the means is a screw compressor including a male rotor having a lobed portion; a female rotor having a lobed portion that engages with the lobed portion of the male rotor; and a casing that accommodates the male rotor and the female rotor. The casing includes: a bore that accommodates the lobed portion of the male rotor and the lobed portion of the female rotor therein such that working chambers on a male rotor side and working chambers on a female rotor side are formed in lobe grooves of the lobed portions; a suction port located on an outer side in a rotor radial direction with respect to the lobed portion of the male rotor and the lobed portion of the female rotor; and a suction flow passage formed so as to connect the suction port to working chambers that are in a suction stroke and communicating in a rotor axial direction with the working chambers that are in the suction stroke. The suction flow passage includes: a male rotor side suction flow passage located on the male rotor side and besides on a downstream side with respect to a virtual plane that passes a central axis of the male rotor and a central axis of the female rotor; and a female rotor side suction flow passage located on the female rotor side and besides on the downstream side with respect to the virtual plane. The male rotor side suction flow passage is formed such that a flow passage wall on the outer side in the rotor radial direction is located at a position same as that of a wall of the bore as viewed from the rotor axial direction at least within a range of one half of an axial pitch of the lobed portion of the male rotor from a suction side end surface of the lobed portion in the rotor axial direction.

Advantage of the Invention

According to the present invention, the pressure loss in the suction flow passage can be reduced.

It is to be noted that problems, configurations and advantages other than those described above are made clear from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view depicting a configuration of a screw compressor of the oil feeding type according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view depicting a structure of a compressor main body in the embodiment of the present invention.

FIG. 3 is a horizontal sectional view taken along line III-III of FIG. 2.

FIG. 4 is a vertical sectional view taken along line IV-IV of FIG. 2.

FIG. 5 is a vertical sectional view taken along line V-V of FIG. 2.

FIG. 6 is a horizontal sectional view depicting a structure of a compressor main body in a modification of the present invention.

MODES FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is described with reference to FIGS. 1 to 5.

The screw compressor of the present embodiment includes a motor 1, a compressor main body 2 driven by the motor 1 to compress air (gas), a gas-liquid separator 3 that separates compressed air discharged from the compressor main body 2 from oil (liquid) included in the compressed air, and an oil pipe 4 that supplies the oil separated by the gas-liquid separator 3 to the compressor main body 2 (particularly, to working chambers, suction side bearings, and discharge side bearings hereinafter described). The oil pipe 4 is provided with an oil cooler 5 for cooling the oil, an oil filter 6 for removing impurities in the oil, and so forth.

The compressor main body 2 includes a male rotor 11A and a female rotor 11B that are screw rotors, and a casing 12 that accommodates the male rotor 11A and the female rotor 11B therein.

The male rotor 11A has a lobed portion 13A having a plurality of (in the present embodiment, four) lobes extending spirally, a suction side shaft portion 14A connected to one side (left side in FIGS. 2 and 3) in an axial direction of the lobed portion 13A, and a discharge side shaft portion 15A connected to the other side (right side in FIGS. 2 and 3) in the axial direction of the lobed portion 13A. The suction side shaft portion 14A of the male rotor 11A is rotatably supported by a suction side bearing 16A, and the discharge side shaft portion 15A of the male rotor 11A is rotatably supported on a discharge side bearing 17A.

Similarly, the female rotor 11B has a lobed portion 13B having a plurality of (in the present embodiment, six) lobes extending spirally, a suction side shaft portion 14B connected to one side (left side in FIGS. 2 and 3), in the axial direction, of the lobed portion 13B, and a discharge side shaft portion 15B connected to the other side (right side in FIGS. 2 and 3), in the axial direction, of the lobed portion 13B. The suction side shaft portion 14B of the female rotor 11B is rotatably supported by a suction side bearing 16B, and the discharge side shaft portion 15B of the female portion 11B is rotatably supported by a discharge side bearing 17B.

The suction side shaft portion 14A of the male rotor 11A extends through the casing 12 and is coupled to a rotary shaft of the motor 1. Thus, the male rotor 11A is rotated by driving of the motor 1, and also the female rotor 11B is rotated through engagement of the lobed portion 13A of the male rotor 11A and the lobed portion 13B of the female rotor 11B.

The casing 12 is configured from a main casing 18, a suction side casing 19 coupled to one side (left side in FIGS. 2 and 3), in the axial direction, of the main casing 18 and a discharge side casing 20 coupled to the opposite side (right side in FIGS. 2 and 3), in the axial direction, of the main casing 18.

The casing 12 has a bore 21 that accommodates the lobed portion 13A of the male rotor 11A and the lobed portion 13B of the female rotor 11B such that working chambers on the male rotor side and working chambers on the female rotor side are formed in lobe grooves of them. The bore 21 is configured such that two cylindrical holes, in which the lobed portion 13A of the male rotor 11A and the lobed portion 13B of the female rotor 11B are individually accommodated, partially overlap with each other.

The casing 12 has a suction port 22 located on the outer side in a rotor radial direction (upper side in FIG. 2) with respect to the lobed portion 13A of the male rotor 11A and the lobed portion 13B of the female rotor 11B, and a suction flow passage 23 formed so as to connect the suction port 22 to working chambers that are in a suction stroke. The bore 21, suction port 22, and suction flow passage 23 are formed in the main casing 18.

The casing 12 has a discharge port 24 located on the outer side (lower side in FIG. 2) in a rotor radial direction with respect to the lobed portion 13A of the male rotor 11A and the lobed portion 13B of the female rotor 11B, and a discharge flow passage 25 formed so as to connect the discharge port to working chambers that are in a discharge stroke. The discharge port 24 is formed in the discharge side casing 20, and the discharge flow passage 25 is formed in the discharge side casing 20 and the main casing 18.

The working chamber is changed in volume while moving from one side to the other side in the rotor axial direction. Consequently, the working chamber sequentially performs a suction stroke for sucking gas from the suction port 22 through the suction flow passage 23, a compression stroke for compressing the gas, and a discharge stroke for discharging the compressed gas to the discharge port 24 through the discharge flow passage 25.

The suction flow passage 23 communicates in the rotor axial direction with working chambers that are in the suction stroke. Further, the suction flow passage 23 has a male rotor side suction flow passage 26A located on the male rotor 11A side and besides on the downstream side (in other words, on the opposite side to the suction port 22) with respect to a virtual plane C that passes the central axis O1 of the male rotor 11A and the central axis O2 of the female rotor 11B, and a female rotor side suction flow passage 26B located on the female rotor 11B side and besides on the downstream side with respect to the virtual plane C (refer to FIGS. 3 and 4).

Here, as a significant characteristic of the present embodiment, a flow passage wall 27A on the outer side, in the rotor radial direction, of the male rotor side suction flow passage 26A (except a portion 28 for confining gas to the working chambers) is formed such that it is located at a position that is the same as that of a wall of the bore 21 as viewed in the rotor axial direction at least within a range of one half of an axial pitch P1 (refer to FIG. 3) of the lobed portion 13A (as a particular example, within a range of P1×0.8=R1 in FIG. 3, within a range of P1×0.5=R1 in FIG. 6 hereinafter described) from a suction side end surface of the lobed portion 13A of the male rotor 11A in the rotor axial direction. It is to be noted that the axial pitch of the lobed portion signifies a distance between lobe tips in the rotor axial direction. Further, since a working error and so forth are taken into consideration, with regard to the flow passage wall 27A, being at the same position as that of the wall of the bore 21 when viewed in the rotor axial direction signifies that the radial position of the flow passage wall 27A with reference to the central axis O1 of the male rotor 11A falls within a range of 95% to 105% of the radial position of the wall of the bore 21.

Further, a flow passage wall 27B on the outer side, in the rotor radial direction, of the female rotor side suction flow passage 26B (except the portion 28 for confining gas to the working chambers) is formed such that it is located at a position that is the same as that of the wall of the bore 21 as viewed in the rotor axial direction at least within a range of one half of an axial pitch P2 (P1=P2; refer to FIG. 3) of the lobed portion 13B from a suction side end surface of the lobed portion 13B of the female rotor 11B in the rotor axial direction (as a particular example, in FIG. 3, within a range of P2×0.8=R2; in FIG. 6 hereinafter described, within a range of P2×0.5=R2). It is to be noted that, since a working error and so forth are taken into consideration, with regard to the flow passage wall 27B, being at the same position as that of the wall of the bore 21 as viewed in the rotor axial direction signifies that the radial position of the flow passage wall 27B with reference to the central axis O2 of the female rotor 11B falls within a range of 95% to 105% of the radial position of the wall of the bore 21.

In such an embodiment as described above, as a component of a flow of gas flowing from the male rotor side suction flow passage 26A to the male rotor side working chamber, a component in the rotor radial direction is less likely to appear, and therefore, the pressure loss can be reduced. Further, since a component of the rotor radial direction is less likely to appear as a component of a flow of gas flowing from the female rotor side suction flow passage 26B to the female rotor side working chamber, the pressure loss can be reduced. As a result, increase in the suction flow amount and reduction of power can be achieved.

Further, in comparison with an alternative case in which the flow passage walls 27A and 27B are located on the outer side in the rotor radial direction with respect to the wall of the bore 21, accumulating of oil into a lower portion of the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B at the time of stop of the compressor main body 2 can be suppressed. Therefore, also the pressure loss by an influence of oil accumulated in a lower portion of the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B can be suppressed.

Supplemental description is given to the reason why the range within which the flow passage walls 27A and 27B are located at the same position as that of the wall of the bore 21 as viewed in the rotor axial direction is determined as a range of at least one half of the axial pitch of the lobed portion of the rotor from the suction side end surface of the lobed portion in the rotor axial direction. From the point of view of the volume efficiency of the screw compressor, it is necessary to take into consideration the area of a rotor axial cross section of the male rotor side suction flow passage 26A with respect to the area of a rotor axial cross section of the male rotor side working chamber (in other words, a cross section extending in the rotor axial direction) and the area of the rotor axial cross section of the female rotor side suction flow passage 26B with respect to the area of the rotor axial cross section of the female rotor side working chamber. Since the area of the rotor axial cross section of the male rotor side working chamber is represented, for example, by (difference between the outer diameter of the lobes of the male rotor and the outer diameter of the shaft) x axial pitch 2, for the area of the rotor axial cross section of the male rotor side suction flow passage 26A, it is better to assure at least (difference between the outer diameter of the lobes of the male rotor and the outer diameter of the shaft) x axial pitch=2. Similarly, since the area of the rotor axial cross section of the female rotor side working chamber is represented, for example, by (difference between the outer diameter of the lobes of the female rotor and the outer diameter of the shaft)×axial pitch=2, for the area of the rotor axial cross section of the female rotor side suction flow passage 26A, it is better to assure at least (difference between the outer diameter of the lobes of the female rotor and the outer diameter of the shaft) x axial pitch=2. From such a point of view, if the male rotor side suction flow passage 26A or the female rotor side suction flow passage 26B does not have the characteristic within at least the range of one half of the axial pitch of the lobed portion from the suction side end surface of the lobed portion of the rotor in the rotor axial direction, a sufficient advantage cannot be obtained.

It is to be noted that, although the embodiment described above is described taking as an example of a case in which the male rotor side suction flow passage 26A is formed such that the area V1 (refer to FIG. 3) of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the male rotor 11A is greater than the area S1 (refer to FIG. 5) of the rotor radial cross section of each working chamber on the male rotor side (in other words, a cross section extending in rotor radial directions), and the female rotor side suction flow passage 26B is formed such that the area V2 (refer to FIG. 3) of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the female rotor 11B is greater than the area S2 (refer to FIG. 5) of the rotor radial cross section of each working chamber on the female rotor side, this is not restrictive. A modification of the present invention is described with reference to FIG. 6. FIG. 6 is a horizontal sectional view representing a structure of a compressor main body in the present modification.

In the present modification, the male rotor side suction flow passage 26A is formed such that the area V1 (refer to FIG. 6) of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the male rotor 11A is the same as the cross sectional area S1 (refer to FIG. 5) in a rotor radial direction of each working chamber on the male water side at least within a range of a rotational pitch (in the present embodiment, 90 degrees) of the lobed portion 13A of the male rotor 11A from the virtual plane C in the direction of rotation of the male rotor 11A. It is to be noted that the rotational pitch of the lobed portion signifies an angle between adjacent lobe tips in the direction of rotor rotation. Further, since a working error and so forth are taken into consideration, the area V1 being the same as the area S1 signifies that the area V1 falls within a range of 95% to 105% of the area S1.

Meanwhile, the female rotor side suction flow passage 26B is formed such that the area V2 (refer to FIG. 6) of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the female rotor 11B is the same as the area S2 (refer to FIG. 5) of the rotor radial cross section of each working chamber on the female rotor side at least within a range of the rotational pitch (in the present embodiment, 45 degrees) of the lobed portion 13B of the female rotor 11B from the virtual plane C in the direction of rotation of the female rotor 11B. It is to be noted that, since a working error and so forth are taken into consideration, the area V2 being the same as the area S2 signifies that the area V2 falls within a range of 95% to 105% of the area S2.

In such a modification as described above, the change in the flow velocity in the male rotor side suction flow passage 26A or the change in the flow velocity from the male rotor side suction flow passage 26A to the male rotor side working chamber can be suppressed to further reduce the pressure loss. Further, the change in the flow velocity in the female rotor side suction flow passage 26B or the change in the flow velocity from the female rotor side suction flow passage 26B to the female rotor side working chamber can be suppressed to further reduce the pressure loss.

It is to be noted that, although the foregoing description of the embodiment is given taking as an example of a case in which both the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B have a first characteristic (more particularly, the characteristic that the flow passage wall on the outer side in the rotor radial direction is located at a position that is the same as that of the wall of the bore 21 as viewed in the rotor axial direction at least within the range of one half of the axial pitch of the lobed portion from the suction side end surface of the lobed portion in the rotor axial direction), this is not restrictive. In particular, only one of the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B may have the first characteristic.

Further, although the foregoing description of the modification is given taking as an example of a case in which both the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B have the first characteristic and a second characteristic (more particularly, the characteristic that they are formed such that the area of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the rotor is the same as the area of the rotor radial cross section of each working chamber at least within the range of the rotational pitch of the lobed portion from the virtual plane C in the direction of rotation of the rotor), this is not restrictive. For example, only one of the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B may have the first characteristic and the second characteristic. Further, for example, both the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B may have the first characteristic while only one of the male rotor side suction flow passage 26A and the female rotor side suction flow passage 26B has the second characteristic.

Further, although the screw compressor of the oil feeding type (more particularly, in which oil is supplied into the working chambers) is taken as an example of the application target of the present invention, this is not restrictive, and the application target of the present invention may be a screw compressor of the water feeding type (more particularly, in which water is supplied into the working chambers) or a screw compressor of the no liquid feeding type (more particularly, in which such liquid as oil or water is not supplied into the working chambers).

DESCRIPTION OF REFERENCE CHARACTERS

11A: Male rotor

11B: Female rotor

12: Casing

13A, 13B: Lobed portion

21: Bore

22: Suction port

23: Suction flow passage

26A: Male rotor side suction flow passage

26B: Female rotor side suction flow passage

27A: Flow passage wall on the outer side, in the rotor radial direction, of male rotor side suction flow passage

27B: Flow passage wall on the outer side, in the rotor radial direction, of female rotor side suction flow passage 

1. A screw compressor, comprising: a male rotor having a lobed portion; a female rotor having a lobed portion that engages with the lobed portion of the male rotor; and a casing that accommodates the male rotor and the female rotor, the casing including a bore that accommodates the lobed portion of the male rotor and the lobed portion of the female rotor therein such that working chambers on a male rotor side and working chambers on a female rotor side are formed in lobe grooves of the lobed portions, a suction port located on an outer side in a rotor radial direction with respect to the lobed portion of the male rotor and the lobed portion of the female rotor, and a suction flow passage formed so as to connect the suction port to working chambers that are in a suction stroke and communicating in a rotor axial direction with the working chambers that are in the suction stroke, the suction flow passage including a male rotor side suction flow passage located on the male rotor side and besides on a downstream side with respect to a virtual plane that passes a central axis of the male rotor and a central axis of the female rotor, and a female rotor side suction flow passage located on the female rotor side and besides on the downstream side with respect to the virtual plane, wherein the male rotor side suction flow passage is formed such that a flow passage wall on the outer side in the rotor radial direction is located at a position same as that of a wall of the bore as viewed in the rotor axial direction at least within a range of one half of an axial pitch of the lobed portion of the male rotor from a suction side end surface of the lobed portion in the rotor axial direction.
 2. The screw compressor according to claim 1, wherein the male rotor side suction flow passage is formed such that an area of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the male rotor is same as an area of a rotor radial cross section of each working chamber on the male rotor side at least within a range of a rotational pitch of the lobed portion of the male rotor from the virtual plane in a direction of rotation of the male rotor.
 3. The screw compressor according to claim 1, wherein the female rotor side suction flow passage is formed such that a flow passage wall on the outer side in the rotor radial direction is located at a position same as that of the wall of the bore as viewed in the rotor axial direction at least within a range of one half of an axial pitch of the lobed portion of the female rotor from a suction side end surface of the lobed portion in the rotor axial direction.
 4. The screw compressor according to claim 3, wherein the female rotor side suction flow passage is formed such that an area of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the female rotor is equal to an area of a rotor radial cross section of each working chamber on the female rotor side at least within a range of a rotational pitch of the lobed portion of the female rotor from the virtual plane in a direction of rotation of the female rotor.
 5. A screw compressor comprising: a male rotor having a lobed portion; a female rotor having a lobed portion that engages with the lobed portion of the male rotor; and a casing that accommodates the male rotor and the female rotor, the casing including a bore that accommodates the lobed portion of the male rotor and the lobed portion of the female rotor therein such that working chambers on a male rotor side and working chambers on a female rotor side are form in lobe grooves of the lobed portions, a suction port located on an outer side in a rotor radial direction with respect to the lobed portion of the male rotor and the lobed portion of the female rotor, and a suction flow passage formed so as to connect the suction port to working chambers that are in a suction stroke and communicating in a rotor axial direction with the working chambers that are in the suction stroke, the suction flow passage including a male rotor side suction flow passage located on the male rotor side and besides on a downstream side with respect to a virtual plane that passes a central axis of the male rotor and a central axis of the female rotor, and a female rotor side suction flow passage located on the female rotor side and besides on the downstream side with respect to the virtual plane, wherein the female rotor side suction flow passage is formed such that a flow passage wall on the outer side in the rotor radial direction is located at a position same as that of a wall of the bore as viewed in a rotor axial direction at least within a range of one half of an axial pitch of the lobed portion of the male rotor from a suction side end surface of the lobed portion in the rotor axial direction.
 6. The screw compressor according to claim 5, wherein the female rotor side suction flow passage is formed such that an area of each flow passage cross section that is a rotor axial cross section taken along each radial direction of the female rotor is same as an area of a rotor radial cross section of each working chamber on the female rotor side at least within a range of a rotational pitch of the lobed portion of the female rotor from the virtual plane in a direction of rotation of the female rotor. 